Topic 4 - Natural Selection and Genetic Modification

Question 1

Describe the work of Darwin and Wallace in the development of the theory of evolution by natural selection

Answer 1

Both developed theories of evolution separately then came together in 1858 to present their findings.

Their theory - NATURAL SELECTION

Individuals of a species show variation meaning some are better to survive in their environment and reproduce healthier offspring. This is natural selection - where the environment (including climate and other organisms) selects which individuals pass on their alleles to the next generation.

Question 2

Explain the impact of Darwin and Wallace’s ideas on modern biology

Answer 2

• it helps us understand the relationships between different species of organisms
• it explains how species evolve
• it explains how different species adapt to changes in their environment

Question 3

Explain Darwin’s theory of evolution by natural selection

Answer 3

1. Adults usually overproduce more young than the environment can support producing a ‘struggle for existence’ by the young
2. Some individuals have inherited advantageous variations in characteristics that are better adapted to the environment. This means a higher chance of survival. However some not adapted as well will be less likely to survive
3. Individuals with advantageous characters pass these genes on to their offspring And they may inherit these characteristics. Ones that didn’t wont produce young.
4. More individuals will have these advantageous variations in the next generation

Question 4

Explain how the emergence of resistant organisms supports Darwin’s theory of evolution including antibiotic resistance in bacteria

Answer 4

Doctors tell you to finish antibiotic courses even if you feel better, and if you do not finish the complete course then the bacteria resistant to the antibiotic can reproduce. This can result in an infection of antibiotic-resistant bacteria that is much harder to treat

Question 5

Describe the evidence for human evolution, based on fossils, including:

a Ardi from 4.4 million years ago
b Lucy from 3.2 million years ago
c Leakey’s discovery of fossils from 1.6 million years ago

Answer 5

Ardi HEIGHT is only 120 cm tall however as it progresses from ardi to Lucy to homo habilis to homo erectus to Homo sapiens the height increases to above 179cm

Pattern of BRAIN SIZE is the same as the height pattern, brain size quickly increases throughout the species.

Skills such as using tools also develop from homo habilis to Homo sapiens - Homo sapiens being able to use the most advanced tools

(Homo habilis, homo erectus and Homo sapiens were all discovered by Leakey)

Question 6

Describe the evidence for human evolution based on stone tools, including:

a the development of stone tools over time
b how these can be dated from their environment

Answer 6

Stone tools give evidence for human evolution as the earliest ones made are around 2.4 million years old and over time more complex tools were made and a greater range of tool types.

These can be dated from their environment by the amount of radiation in samples of sediment just above and below the layer in which the tools are found can be used to date the sediment and so give a range of dates when the tools were left there.

Question 7

Describe how the anatomy of the pentadactyl limb provides scientists with evidence for evolution

Answer 7

Many living vertebrates have the same pentadactyl (five fingered) limb structure and it would be highly unlikely that they had all evolved from different ancestors and have a similar bone arrangement.

Question 8

Describe how genetic analysis has led to the suggestion of the three domains rather than the five kingdoms classification method

Answer 8

Genetic research shows that the organisms which were grouped as prokaryotes in the kingdom system should be separated into two groups, which have been named EUBACTERIA and ARCHAEA.

This is because the genes of organisms in archaea work more like those in the eukaryotes, while the genes of organisms in eubacteria work a little differently. This grouping forms the three domain system of classification

Question 9

Explain selective breeding

Answer 9

Selective breeding is when plants or animals with certain desirable characteristics are chosen to breed together, so that offspring will be produced that inherit these characteristics, producing new breeds and varieties of plants and animals.

Selective breeding has taken place over thousands of years, but more recently genetic engineering has been developed as a way of manipulating genetics

Question 10

Describe reasons for selective breeding

Answer 10

• disease resistance
• increased yield
• better ability to cope with difficult conditions
• faster growth
• better flavour

Question 11

Describe what tissue culture can be used for

Answer 11

Plant and animal tissue can be used to produce cell cultures. This means you can make many identical copies of a special organism, for example one that has been genetically modified. It can also mean drugs can be tested on cell cultures instead of animals.

Question 12

Describe the process of tissue culture

Answer 12

1. Tissue sample cut from parent plant
2. Agar jelly containing plant hormones and nutrients
3. Samples grow into tiny plants
4. Trays of compost

This process is similar to other kinds of cells

Question 13

Explain the advantages off plant and animal tissue culture in medical research and plant breeding programmes

Answer 13

ADVANTAGES OF USING ANIMAL CELL CULTURES:

• test the effect of drugs and other chemicals on cells
• check for cancer cells in a sample from a patient
• produce important proteins, eg antibodies

ADVANTAGES OF USING PLANT CELL CULTURES:

• produce hundreds or thousands of identical plants (clones) from just one parents plant, eg genetically modified plants
• cells can be grown in culture to make plant products, eg paclitaxel used to treat cancer

Question 14

Describe genetic engineering

Answer 14

GENETIC ENGINEERING is changing the genome (the DNA) of an organism, often by introducing genes from another to create genetically modified organisms (GMOs)

Question 15

Explain how the process of genetic engineering works

Answer 15

Genes can be transferred from any kind of organism to any other kind of organism , eg bacteria, humans, other animals, plants

1. The gene for a characteristic is ‘cut out’ of a chromosome using enzymes
2. The gene is inserted into a chromosome inside the nucleus of a cell in a different organism
3. The cell of this organism now produces the characteristic from the gene

Question 16

Explain the process of making human insulin using genetic engineering

Answer 16

1. DNA from a human cell is cut into pieces using enzymes called RESTRICTION ENZYMES. These leave behind STICKY ENDS (unpaired bases)
2. Bacteria cells contain small circles of DNA called plasmids. The same restriction enzymes are used to cut plasmids open, leaving sticky ends with matching sets of unpaired bases.
3. The pieces of DNA containing the insulin gene are mixed with the plasmids. The bases in the sticky ends pair up. An enzyme called DNA ligase is added, linking the DNA back into a continuous circle
4. The plasmids are inserted into bacteria. The bacteria can now be grown in huge fermenters, where they make human insulin

A VECTOR is the name for anything that carries the new gene into a cell. In the case with insulin, the vector is a plasmid. Other kids of vectors may be used, such as viruses

Question 17

Explain the advantages and disadvantages of genetic engineering to produce GM organisms including the modification of crop plants

Answer 17

GM crop plants have been genetically modified to give them new characteristics eg:
- resistance to attack by insects
- resistance to herbicides, so that fields can be sprayed to kill weeds, but not the crop
These characteristics can help the crop grow better and produce more food (an increased yield)

However in some cases it may be unethical to use animals for the benefit of humans (help treat diseases, better nutrition benefit from eating them)

Question 18

Explain how genetic engineering is used to create insect resistant plants from the bacterium Bacillus thuringiensis

Answer 18

1. The bacterium Bt (Bacillus thuringiensis) naturally produces a chemical that is poisonous to insect pests such as caterpillars. This chemical is called Bt toxin.
2. The gene for Bt toxin can be cut out of the bacterial DNA and inserted into the DNA of a plant cell using agrobacterium tumefaciens (naturally infects plant cells, and so is a useful vector for making transgenic plants)
3. Plants grown from these cells produce the Bt toxin. When an insect tries to eat them, the poison kills the insect pest

Question 19

Explain advantages and disadvantages of using Bt plants

Answer 19

ADVANTAGES:

• Crop damage is reduced so crop yield should increase
• less chemical insecticide is needed so other harmless and useful insects are less likely to be harmed (better for biodiversity)

DISADVANTAGES:

• seed from transgenic plants is more expensive than seed from non transgenic varieties
• insect pests may become resistant to Bt toxin
• Bt gene may transfer to closely related wild plants by pollination, which would make those plants resistant to pests too

Question 20

Explain the advantages and disadvantages of fertilisers

Answer 20

ADVANTAGES:

• fertilisers contain nutrients, including nitrogen, phosphorus, and potassium, that help crops to grow well
• they increase crop yields providing more food for people
• it is a good way to use animal waste (manure) from farms

DISADVANTAGES:

• excess fertiliser can pollute waterways, causing eutrophication
• artificial fertilisers can be expensive to make
• artificial fertilisers can reduce soil biodiversity

Question 21

Explain the advantages and disadvantages of biological control

Answer 21

ADVANTAGES:

• the pest cannot become resistant
• if well chosen, the control agent is specific to the pest
• avoids using chemical pesticides which can leave harmful residues and kill useful organisms

DISADVANTAGES:

• biological control doesn’t get ride of the pest completely
• the control agent may become a pest itself